1. Field of the Invention
This invention relates to a wireless communication system using light wave, radio wave, or the like.
2. Description of the Prior Art
In a wired LAN (local area network), terminal devices are connected to each other via wires. The terminal devices can communicate with each other via the wires.
It is known to combine a wired LAN and a wireless communication network. For example, a wired LAN is additionally provided with an access point device (a gateway device) which can execute both wired communication and wireless communication. The access point device is connected via wires to normal terminal devices in the wired LAN. The access point device can communicate with the normal terminal devices in the wired LAN via the wires. Also, the access point device can execute wireless communication with terminal devices in a wireless communication network. In this case, the wired LAN and the wireless communication network are connected via the access point device (the gateway device). In addition, the access point device is a member of the wired LAN as well as a member of the wireless communication network.
In a wireless communication network, if two terminal devices simultaneously transmit wireless signals toward another terminal device, the transmitted wireless signals collide with each other. In this case, both the transmission-side terminal devices fail to normally communicate with the reception-side terminal device.
There is a wireless communication network of a CSMA (carrier sense multiple access) type. In the CSMA wireless communication network, when a terminal device is required to transmit a wireless signal, the terminal device executes a process of sensing a carrier to check whether a communication channel is occupied or unoccupied. When the communication channel is unoccupied, the terminal device executes the transmission of the wireless signal. When the communication channel is occupied, the terminal device falls into a stand-by state to avoid a signal collision.
In a wired LAN, if two terminal devices simultaneously transmit signals toward another terminal device via a common bus wire, the transmitted signals collide with each other. In this case, both the transmission-side terminal devices fail to normally communicate with the reception-side terminal device.
There is a wired LAN of a CD (collision detection) type. In such a wired LAN, every terminal device monitors the level of a voltage at a common bus wire to check whether the common bus wire is occupied or unoccupied. The information of whether the common bus wire is occupied or unoccupied is used in avoiding a signal collision.
There is a wired LAN having a star connection between a hub device and terminal devices. The connection between the hub device and each terminal device includes a duplex line. Such a wired LAN intrinsically has a function of avoiding a signal collision.